Thanks for taking the time to provide feedback! It's evident that you've spent quite a bit of time with the game, and it's always good to hear from players who have played the game enough to have an understanding and offer a critique of the core gameplay systems. We'll take it all under advisement, and some of the things you mentioned in your post are things we're currently working on.
We've made some changes to idol recruitment with the latest update (which just shipped earlier today), which might address some of the concerns you have in that area. Also, there are new training policies that allow you to control auto-practice in a more fine-tuned manner; you might find these potentially helpful.
Also address one thing you specifically mentioned in your post:
- [Bug] Stylists do not respect the stamina threshold like dance and vocals coaches do.
This is not a bug. Idols don't consume stamina from sitting in the stylist's chair (whereas they do consume stamina while doing dance or vocal practice), so the game will allow them to be styled regardless of their current stamina level; this is the intended behavior.